1. Field of the Invention
The present invention relates generally to the field of image processing, and particularly to a technique for setting a region of interest (RO) of an image in an electronic processing apparatus such as an electronic camera.
2. Description of the Related Art
In an electronic apparatus such as a digital camera, a captured image is usually compressed before it is recorded on a recording medium.
Presently, JPEG is widely used for compressing image data; however, a significant amount of research is being done to promote the use of a new image compression technique, JPEG 2000 (ISO/IEC FCD 15444-1). JPEG 2000 has a selective region image quality improvement function (ROI function) for reducing the compression rate (improving the image quality) of a region of interest (ROI) of an image without reducing the compression rate of the overall image.
This ROI function is particularly appealing to an electronic camera. By setting an important region of a captured image as the ROI, high image quality can be maintained in the important region while the amount of data of the overall image other than the important region can be significantly reduced.
To use the ROI function, it is necessary to specify an ROI in each individual captured image. A publicly known technique for specifying the ROI is disclosed in Japanese Patent Laid-Open Publication No. 2001-230947, for example. In this Japanese application, an electronic camera having an EVF (electronic view finder) screen that displays a guidance frame or a template image is disclosed. The guidance frame or template image is used as a base image for framing and capturing an image. Then, a region within the guidance frame or a region other than the template image is handled as the ROI in the compression process of the captured image. Also, the ROI information is recorded on a header of a corresponding image file, and thus the ROI can be displayed on the rest of the reproduced image in the image reproduction process.
Also, Japanese Patent Laid-Open Publication No. 2001-119625 discloses a digital camera that determines a range of a main object of a captured image based on a user operation, handles this range as an ROI, compresses the corresponding range at a lower compression rate than that for the rest of the regions, and describes the ROI information on a header of a corresponding compressed image file. This Japanese patent application mentions that the range of the main object may be determined automatically based on edge or histogram information of the image. However, there appears to be no mention of JPEG 2000 in this Japanese patent application.
The ROI setting method using a guidance frame or a template image as disclosed in Japanese Patent Laid-Open Publication No. 2001-230947 limits the flexibility of the framing and scene capturing operation.
Also, with the method of manually setting the range of the main object as the ROI as disclosed in Japanese Patent Laid-Open Publication No. 2001-119625, there is a problem in that the manual operation can be quite troublesome and the method may not be used for successive capturing of still images or capturing of moving images. Although mention is made of automatically determining the range of the main object based on the edge or histogram of the image, a specific method for determining the ROI does not appear to be disclosed in this Japanese patent application. The legitimacy of the determined ROI depends upon such factor as this determination method.
Also, generally speaking, a wide variety of scene capturing operations need to be considered in automating the ROI setting operation. Further, since user preferences may vary considerably, it may be more practical to enable a user to intervene in the capturing operation to a certain degree.